VB.NET BackgroundWorker.CancellationPending屬性代碼示例

' Abort the operation if the user has canceled.
' Note that a call to CancelAsync may have set 
' CancellationPending to true just after the
' last invocation of this method exits, so this 
' code will not have the opportunity to set the 
' DoWorkEventArgs.Cancel flag to true. This means
' that RunWorkerCompletedEventArgs.Cancelled will
' not be set to true in your RunWorkerCompleted
' event handler. This is a race condition.
If worker.CancellationPending Then
    e.Cancel = True
Else
    If n < 2 Then
        result = 1
    Else
        result = ComputeFibonacci(n - 1, worker, e) + _
                 ComputeFibonacci(n - 2, worker, e)
    End If

    ' Report progress as a percentage of the total task.
    Dim percentComplete As Integer = _
        CSng(n) / CSng(numberToCompute) * 100
    If percentComplete > highestPercentageReached Then
        highestPercentageReached = percentComplete
        worker.ReportProgress(percentComplete)
    End If

End If

' 導入命名空間
Imports System
Imports System.Data
Imports System.Collections
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Data.SqlClient

public class MainClass
   Shared Sub Main()
       Dim form1 As Form = New Form1
       Application.Run(form1)
   End Sub
End Class


Public Class Form1
    Private Sub btnStartProcess_Click(ByVal sender As System.Object, _
     ByVal e As System.EventArgs) Handles btnStartProcess.Click

        btnStartProcess.Enabled = False
        btnCancel.Enabled = True
        prgLongProcess.Value = 0

        bgrLongProcess.WorkerReportsProgress = True
        bgrLongProcess.WorkerSupportsCancellation = True
        bgrLongProcess.RunWorkerAsync()
    End Sub

    Private Sub btnCancel_Click(ByVal sender As System.Object, _
     ByVal e As System.EventArgs) Handles btnCancel.Click
        bgrLongProcess.CancelAsync()
    End Sub

    Private Sub bgrLongProcess_ProgressChanged(ByVal sender As Object, _
     ByVal e As System.ComponentModel.ProgressChangedEventArgs) _
     Handles bgrLongProcess.ProgressChanged
        prgLongProcess.Value = e.ProgressPercentage
    End Sub

    Private Sub bgrLongProcess_RunWorkerCompleted(ByVal sender As Object, _
     ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) _
     Handles bgrLongProcess.RunWorkerCompleted
        btnStartProcess.Enabled = True
        btnCancel.Enabled = False
    End Sub

    Private Sub bgrLongProcess_DoWork(ByVal sender As Object, _
     ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgrLongProcess.DoWork
        For i As Integer = 1 To 10000

            For j As Integer = 1 To 10000

            Next j
            If bgrLongProcess.CancellationPending Then Exit Sub

            bgrLongProcess.ReportProgress(CInt(100 * i / 10000))
        Next i
    End Sub

End Class



<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Public Class Form1
    Inherits System.Windows.Forms.Form

    'Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.btnStartProcess = New System.Windows.Forms.Button
        Me.btnCancel = New System.Windows.Forms.Button
        Me.prgLongProcess = New System.Windows.Forms.ProgressBar
        Me.bgrLongProcess = New System.ComponentModel.BackgroundWorker
        Me.SuspendLayout()
        '
        'btnStartProcess
        '
        Me.btnStartProcess.Location = New System.Drawing.Point(8, 8)
        Me.btnStartProcess.Name = "btnStartProcess"
        Me.btnStartProcess.Size = New System.Drawing.Size(75, 23)
        Me.btnStartProcess.TabIndex = 0
        Me.btnStartProcess.Text = "Start"
        '
        'btnCancel
        '
        Me.btnCancel.Location = New System.Drawing.Point(208, 8)
        Me.btnCancel.Name = "btnCancel"
        Me.btnCancel.Size = New System.Drawing.Size(72, 24)
        Me.btnCancel.TabIndex = 1
        Me.btnCancel.Text = "Cancel"
 
        Me.prgLongProcess.Location = New System.Drawing.Point(8, 48)
        Me.prgLongProcess.Name = "prgLongProcess"
        Me.prgLongProcess.Size = New System.Drawing.Size(272, 16)
        Me.prgLongProcess.TabIndex = 2

        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(288, 75)
        Me.Controls.Add(Me.prgLongProcess)
        Me.Controls.Add(Me.btnCancel)
        Me.Controls.Add(Me.btnStartProcess)

        Me.Text = "UseBackgroundWorker"
        Me.ResumeLayout(False)

    End Sub
    Friend WithEvents btnStartProcess As System.Windows.Forms.Button
    Friend WithEvents btnCancel As System.Windows.Forms.Button
    Friend WithEvents prgLongProcess As System.Windows.Forms.ProgressBar
    Friend WithEvents bgrLongProcess As System.ComponentModel.BackgroundWorker

End Class